It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It could be a fuel pump acting up, would have to verify by Teeing in a fuel gauge and monitoring fuel pressure when the car won't start. It could be a relay or electrical issue. I have a friend's Jeep right now that the computer is failing in, when it stalls I have hit the computer with my fist and it starts right up. The company I sent the computer to said the found a fault on the ECU board. Too many possibilities to guess at without being able to do tests to confirm what is wrong.